CN109295330B - Method for refining nitride inclusions in nickel-based wrought superalloy - Google Patents

Abstract

A method for refining nitride-based inclusions in nickel-based deformed superalloy, the steps are as follows: (1) surface pretreatment of metal raw materials; (2) vacuum induction melting: Ni, Cr, Co, W, Mo, etc. Put it into a crucible and vacuumize it; add C, Nb, Ti, Al after melting; fill with argon, add B and Zr, and pour it into a steel mold after complete melting to obtain a superalloy electrode; (3) Vacuum electroslag remelting : Using slag material containing 0.01-0.5wt.% MgO, vacuuming to 0.01-100Pa, then filling with high-purity argon to 0.01-0.06MPa; slag removal, refining. The invention utilizes the metallurgical reaction of molten slag and alloy liquid during electroslag remelting to form fine and uniformly distributed MgO-based inclusions, providing a core for the subsequent formation of nitride-based inclusions; the size of nitride-based inclusions is reduced, and the distribution of more uniform. Vacuum electroslag remelting can reduce the number of nitride-based inclusions; by controlling the MgO content in electroslag and the process parameters of electroslag remelting, the Mg content in the alloy and the number and size of Mg-based oxide inclusions can be precisely controlled. The process is stable and the cost is low.

Description

A method for refining nitride-based inclusions in nickel-based deformed superalloys

technical field

The invention belongs to the field of preparation of superalloys, and more particularly relates to a method for refining nitride-based inclusions in nickel-based deformed superalloys by using an electroslag remelting process.

Background technique

Superalloys are alloys whose service temperature exceeds 650°C and have good thermal stability and thermal strength. According to its production process, it can be divided into three categories: deformed superalloy, cast superalloy and powder metallurgy superalloy. According to its composition, it can be divided into three categories: nickel-based superalloy, cobalt-based superalloy and iron-based superalloy. Among them, the nickel-based deformed superalloy has good mechanical properties and comprehensive strength and toughness indicators, as well as good thermal fatigue resistance, thermal corrosion resistance and wear resistance. Therefore, it is widely used in aerospace, aviation, nuclear energy, petroleum and other fields.

Nickel-based wrought superalloys usually contain Ti as a strengthening element, and high strength is achieved by the precipitation of Ni ₃ (Al,Ti) and Ni ₃ Ti intermetallic compounds through aging treatment. However, Ti is a strong nitride and carbide forming element, and nitride-based inclusions such as TiN and TiCN are easily formed during the melting and solidification of the alloy. Moreover, such inclusions often exist in the shape of cuboids or cubes with sharp corners. If the inclusions are small in size, they are hardly the starting point for fatigue failure of the superalloy. However, if the inclusion size is large, it may cause fatigue failure. Moreover, such inclusions can hardly be eliminated during forging deformation and heat treatment.

The formation of nitride-based inclusions such as TiN and TiCN includes two stages of nucleation and growth. The nucleation methods include homogeneous nucleation and heterogeneous nucleation. Homogeneous nucleation relies on its own energy fluctuations and structural fluctuations for nucleation. Heterogeneous nucleation is nucleation by means of other existing particles, such as MgO, Al ₂ O ₃ and other oxide-based inclusions that already exist in the alloy liquid. Therefore, the purpose of the present invention is to find a method for refining nitride-based inclusions from the perspective of nucleation and growth, thereby reducing the size of such inclusions and improving the service life of parts.

Electroslag remelting technology has significant advantages in removing foreign inclusions and large inclusions. At the same time, electroslag remelting has the characteristics of sequential solidification, rapid cooling, dense structure and uniform distribution of endogenous inclusions. During the electroslag remelting process, the molten slag undergoes a metallurgical reaction with the alloy liquid. During the electroslag remelting of superalloys, Al and Ti in the alloy liquid react with MgO in the slag to generate dissolved magnesium into the alloy liquid. Since dissolved magnesium has a strong ability to combine with oxygen, small-sized MgO-based inclusions (MgO-Al ₂ O ₃ , MgO-Al ₂ O ₃ -TiO ₂ , etc.) will appear in the alloy liquid. Based on the above-mentioned metallurgical reaction, the present invention proposes to add an appropriate amount of MgO to the slag to provide a core for the formation of nitride-based inclusions, so as to make them heterogeneously nucleated, so as to achieve the purpose of refining the nitride-based inclusions. Since ordinary electroslag remelting is not protected by argon gas and vacuum atmosphere, and the nitrogen content is relatively high, the present invention adopts vacuum electroslag remelting. Moreover, vacuum electroslag remelting can control the oxygen content below 10ppm. When it exceeds 10 ppm, the oxide tends to grow.

It should be noted, however, that nitrogen is a core element for forming nitride-based inclusions. Therefore, the most direct measure to reduce the harm of such inclusions is to reduce the nitrogen content, thereby reducing its quantity. Therefore, the N content in the alloy should be below the level of 0.0015 wt.%. In the present invention, on the basis of reducing the number of nitride-based inclusions, the micronization treatment is performed.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for refining nitride-based inclusions in nickel-based deformed superalloys, aiming to reduce the size of nitride-based inclusions in nickel-based deformed superalloys and improve the service life of components.

The nickel-based deformed superalloy involved in the present invention has a chemical composition range including the nickel-based deformed superalloy and other non-standard grades of nickel in the standard "GB/T 14992-2005 Classification and Designation of High-Temperature Materials of Superalloys and Intermetallic Compounds" Base deformed superalloy. The specific process steps are:

(1) Surface pretreatment of raw materials: Surface pretreatment of bulk pure nickel, pure chromium, pure cobalt, pure tungsten, pure molybdenum, pure niobium, and pure aluminum, pure titanium, pure iron and other metal raw materials. First, perform pretreatment in 5vol.% hydrochloric acid aqueous solution to remove surface oxides, and the pretreatment time is 20-30min; then put it in absolute ethanol for ultrasonic treatment, and the treatment time is 10-20min; the purity of various raw materials is greater than 99.9%;

(2) Vacuum induction smelting: Weigh various metal raw materials and other non-metallic raw materials in step (1) in proportion, and first place metal blocks such as Ni, Cr, Co, W, Mo and other elements with low affinity with O and N. Put it into a crucible for vacuum induction melting for vacuum melting; add C, Nb, Ti, Al, B, Zr, etc. after melting; pour it into a steel mold after complete melting to obtain a superalloy electrode; the material of the crucible is alumina;

(3) Vacuum electroslag remelting: using the electrode obtained in step (2) as a consumable electrode, an arc ignition agent is prepared with CaF ₂ and TiO ₂ with a mass ratio of 0.9:1 to 1.1:1; the slag is pre-melted Treated, mechanically pulverized, and then spread on the bottom of the crystallizer; the weight of each slag material is 3-5wt.% of the electrode weight; put into the consumable electrode prepared in step (2); Pure argon gas to 0.01-0.06MPa; slag arcing; arc-starting current is 800-1500A, normal smelting current is 2000-3000A, and voltage is 35-45V.

Further, the vacuum induction melting described in step (2) is characterized in that: vacuumize to 5×10 ^-1 Pa～ ⁵ ×10 ^-3 Pa, and carry out melting; after the melt is melted, add C, and refine for 15 to 30 minutes ; Add strong nitride and oxide forming elements Nb, Ti, Al, and heat until the added material is completely melted; fill with argon to 0.01-0.06MPa, add easily burnt and volatile trace elements B and Zr, and stir at the same time , until the alloy liquid is completely melted again and poured into the steel mold.

Further, the vacuum induction melting in step (2) is characterized in that: a high-purity alumina crucible is used, and the MgO content is less than 0.0010wt.%.

Further, the vacuum electroslag remelting in step (3) is characterized in that: the proportion of slag materials is 10-30wt.% CaO, 10-30wt.% Al ₂ O ₃ , 0.01-0.5wt.% MgO, and the rest the amount of CaF ₂ ; the slag raw materials are proportioned and mixed uniformly, and then melted between 1300 and 1700 ° C for 10 to 30 minutes to ensure the uniformity and clarification of the liquid slag; poured into a metal mold for cooling; mechanically pulverized After screening, the particle size is 1-15mm; bake at 600-800℃ for at least 8h before use.

Further, the maximum size of the nitride-based inclusions in the nickel-based deformed superalloy prepared by the present invention is 6 μm, and the average size is less than 3.3 μm.

The advantages of the present invention are: (1) The metallurgical reaction between the molten slag and the alloy liquid during electroslag remelting is used to form fine and uniformly distributed MgO series inclusions (MgO-Al ₂ O ₃ , MgO-Al ₂ O ₃ -TiO ₂ , etc.), providing a core for the subsequent formation of nitride-based inclusions; (2) vacuum electroslag remelting can obtain low nitrogen content, thereby reducing the number of nitride-based inclusions; (3) by controlling MgO in electroslag The content and process parameters of electroslag remelting can precisely control the Mg content and the number and size of Mg-based oxide inclusions in the alloy, and the process is stable; (4) The distribution of nitride-based inclusions is more uniform.

Description of drawings

FIG. 1 is a scanning electron microscope photograph of a cross section of a nitride-based inclusion having an MgO core.

FIG. 2 is a scanning electron microscope photograph of a single nitride-based inclusion.

Detailed ways

Example 1: GH4169 nickel-based deformed superalloy

(1) Raw material pretreatment process: use bulk pure nickel, pure chromium, pure cobalt, pure tungsten, pure molybdenum, pure niobium, pure aluminum, pure titanium, high-purity graphite, boron, zirconium, etc. The purity is greater than 99.9%; the metal raw materials are pretreated in 5vol.% hydrochloric acid aqueous solution to remove surface oxides, and the pretreatment time is 25min; then various metal raw materials are placed in absolute ethanol for ultrasonic treatment, and the treatment time is 15min .

(2) Vacuum induction melting process: first put elements Ni, Cr, Co, W, Mo, Fe with low affinity with O and N into the crucible of the vacuum induction melting furnace; evacuate to 5×10 ^-2 Pa, Smelting; after the melt is melted, add C, and refine for 25 minutes; add strong nitride and oxide forming elements Nb, Ti, Al, and heat until the added material is completely melted; fill with argon to 0.02MPa, and finally add easy burning and the volatile trace elements B and Zr, stirring at the same time until the alloy liquid is completely melted again and then poured into a steel mold to obtain a superalloy electrode; the electrode is machined to remove the surface oxide scale and riser to complete the electrode rod. Preparation;

(3) Vacuum electroslag remelting process: Weld the electrode rod to the special dummy electrode; prepare the arc starting agent with CaF ₂ and TiO ₂ with a mass ratio of 0.9:1-1.1:1; the slag material ratio is 30wt.% CaO, 30wt.% Al ₂ O ₃ , 0.2wt.% MgO, balance CaF ₂ ; the weight of each slag material is 3wt.% of the electrode weight; Then spread it on the bottom of the crystallizer, evacuate it to 1Pa, and then fill it with high-purity argon to 0.05MPa, and the slag will start arcing. The arc ignition current is 1000A, the normal smelting current is 2000~3000A, and the voltage is 35~45V.

In order to examine the effect of the present invention, an experiment of a comparative example was carried out. In the comparative experiment, vacuum electroslag remelting was performed without adding MgO to the slag, and other experimental conditions were the same.

Metallographic samples were collected from both ends of the electroslag ingots of Examples and Comparative Examples of the present invention. After grinding and polishing the metallographic samples, a fully automatic analysis of inclusions was performed on a scanning electron microscope (ZEISS, EVO18) with an energy dispersive spectrometer (Oxford equipment, INCA). This automatic inclusion analysis system has the characteristics of efficient, fast and accurate measurement of the size, shape and chemical composition of inclusions in the sample, and the analysis results can obtain the statistical data of all non-metallic inclusions in the sample.

FIG. 1 is a scanning electron microscope photograph of a cross section of a nitride-based inclusion having an MgO core obtained by the present invention, and FIG. 2 is a scanning electron microscope photograph of a nitride-based inclusion obtained by a comparative example. Table 1 shows the Mg content and the size of nitride-based inclusions in the GH4169 superalloy electroslag ingot. It can be seen that the present invention enables the size reduction of the nitride-based inclusions.

Table 1: Chemical Composition and Inclusion Test Results

Example 2: GH4169 nickel-based deformed superalloy

(1) Raw material pretreatment process: use bulk pure nickel, pure chromium, pure cobalt, pure tungsten, pure molybdenum, pure niobium, pure aluminum, pure titanium, high-purity graphite, boron, zirconium, etc. The purity is greater than 99.9%; the metal raw materials are pretreated in 5vol.% hydrochloric acid aqueous solution to remove surface oxides, and the pretreatment time is 25min; then various metal raw materials are placed in absolute ethanol for ultrasonic treatment, and the treatment time is 15min .

(2) Vacuum induction melting process: first put elements Ni, Cr, Co, W, Mo, Fe with low affinity with O and N into the crucible of the vacuum induction melting furnace; evacuate to 5×10 ^-2 Pa, Smelting; after the melt is melted, add C, and refine for 20 minutes; add strong nitride and oxide forming elements Nb, Ti, Al, and heat until the added material is completely melted; fill with argon to 0.05MPa, and finally add easy burning and the volatile trace elements B and Zr, stirring at the same time until the alloy liquid is completely melted again and then poured into a steel mold to obtain a superalloy electrode; the electrode is machined to remove the surface oxide scale and riser to complete the electrode rod. Preparation;

(3) Vacuum electroslag remelting process: Weld the electrode rod to the special dummy electrode; prepare the arc starting agent with CaF ₂ and TiO ₂ with a mass ratio of 0.9:1-1.1:1; the slag material ratio is 20wt.% CaO, 20wt.% Al ₂ O ₃ , 0.3wt.% MgO, balance CaF ₂ ; the weight of each slag material is 4wt.% of the electrode weight; Then spread it on the bottom of the crystallizer, evacuate it to 1Pa, and then fill it with high-purity argon to 0.05MPa, and the slag will start arcing. The arc ignition current is 1200A, the normal smelting current is 2000~3000A, and the voltage is 35~45V.

In order to examine the effect of the present invention, an experiment of a comparative example was carried out. In the comparative experiment, vacuum electroslag remelting was performed without adding MgO to the slag, and other experimental conditions were the same.

Metallographic samples were collected from both ends of the electroslag ingots of Examples and Comparative Examples of the present invention. After grinding and polishing the metallographic samples, a fully automatic analysis of inclusions was performed on a scanning electron microscope (ZEISS, EVO18) with an energy dispersive spectrometer (Oxford equipment, INCA). Table 2 shows the Mg content and the size of nitride-based inclusions in the GH4169 superalloy electroslag ingot. It can be seen that the present invention enables the size reduction of the nitride-based inclusions.

Table 2: Chemical Composition and Inclusion Test Results

Example 3: GH4220 nickel-based deformed superalloy

(1) Raw material pretreatment process: use bulk pure nickel, pure chromium, pure cobalt, pure tungsten, pure molybdenum, pure niobium, pure aluminum, pure titanium, high-purity graphite, boron, zirconium, etc. The purity is greater than 99.9%; the metal raw materials are pretreated in 5vol.% hydrochloric acid aqueous solution to remove surface oxides, and the pretreatment time is 25min; then various metal raw materials are placed in absolute ethanol for ultrasonic treatment, and the treatment time is 15min .

(2) Vacuum induction melting process: first put elements Ni, Cr, Co, W, Mo, Fe with low affinity with O and N into the crucible of the vacuum induction melting furnace; evacuate to 5×10 ^-2 Pa, Smelting; after the melt is melted, add C, and refine for 25 minutes; add strong nitride and oxide forming elements Nb, Ti, Al, and heat until the added material is completely melted; fill with argon to 0.02MPa, and finally add easy burning and the volatile trace elements B and Zr, stirring at the same time until the alloy liquid is completely melted again and then poured into a steel mold to obtain a superalloy electrode; the electrode is machined to remove the surface oxide scale and riser to complete the electrode rod. Preparation;

(3) Vacuum electroslag remelting process: Weld the electrode rod to the special dummy electrode; prepare the arc starting agent with CaF ₂ and TiO ₂ with a mass ratio of 0.9:1-1.1:1; the slag material ratio is 25wt.% CaO, 25wt.% Al ₂ O ₃ , 0.2wt.% MgO, the balance CaF ₂ ; the weight of each slag material is 3wt.% of the electrode weight; Then spread it on the bottom of the crystallizer, evacuate it to 1Pa, and then fill it with high-purity argon to 0.05MPa, and the slag will start arcing. The arc ignition current is 1000A, the normal smelting current is 2000~3000A, and the voltage is 35~45V.

In order to examine the effect of the present invention, an experiment of a comparative example was carried out. In the comparative experiment, vacuum electroslag remelting was performed without adding MgO to the slag, and other experimental conditions were the same.

Metallographic samples were collected from both ends of the electroslag ingots of Examples and Comparative Examples of the present invention. After grinding and polishing the metallographic samples, a fully automatic analysis of inclusions was performed on a scanning electron microscope (ZEISS, EVO18) with an energy dispersive spectrometer (Oxford equipment, INCA). Table 3 shows the Mg content and the size of nitride-based inclusions in the GH4220 superalloy electroslag ingot. It can be seen that the present invention enables the size reduction of the nitride-based inclusions.

Table 3: Chemical Composition and Inclusion Test Results

Example 4: GH4220 nickel-based deformed superalloy

(1) Raw material pretreatment process: use bulk pure nickel, pure chromium, pure cobalt, pure tungsten, pure molybdenum, pure niobium, pure aluminum, pure titanium, high-purity graphite, boron, zirconium, etc. The purity is greater than 99.9%; the metal raw materials are pretreated in 5vol.% hydrochloric acid aqueous solution to remove surface oxides, and the pretreatment time is 25min; then various metal raw materials are placed in absolute ethanol for ultrasonic treatment, and the treatment time is 15min .

(2) Vacuum induction melting process: first put elements Ni, Cr, Co, W, Mo, Fe with low affinity with O and N into the crucible of the vacuum induction melting furnace; evacuate to 5×10 ^-2 Pa, Smelting; after the melt is melted, add C, and refine for 20 minutes; add strong nitride and oxide forming elements Nb, Ti, Al, and heat until the added material is completely melted; fill with argon to 0.05MPa, and finally add easy burning and the volatile trace elements B and Zr, stirring at the same time until the alloy liquid is completely melted again and then poured into a steel mold to obtain a superalloy electrode; the electrode is machined to remove the surface oxide scale and riser to complete the electrode rod. Preparation;

(3) Vacuum electroslag remelting process: Weld the electrode rod to the special dummy electrode; prepare the arc starting agent with CaF ₂ and TiO ₂ with a mass ratio of 0.9:1-1.1:1; the slag material ratio is 20wt.% CaO, 20wt.% Al ₂ O ₃ , 0.3wt.% MgO, balance CaF ₂ ; the weight of each slag material is 4wt.% of the electrode weight; Then spread it on the bottom of the crystallizer, evacuate it to 1Pa, and then fill it with high-purity argon to 0.05MPa, and the slag will start arcing. The arc ignition current is 1200A, the normal smelting current is 2000~3000A, and the voltage is 35~45V.

In order to examine the effect of the present invention, an experiment of a comparative example was carried out. In the comparative experiment, vacuum electroslag remelting was performed without adding MgO to the slag, and other experimental conditions were the same.

Metallographic samples were collected from both ends of the electroslag ingots of Examples and Comparative Examples of the present invention. After grinding and polishing the metallographic samples, a fully automatic analysis of inclusions was performed on a scanning electron microscope (ZEISS, EVO18) with an energy dispersive spectrometer (Oxford equipment, INCA). Table 4 shows the Mg content and the size of nitride-based inclusions in the GH4220 superalloy electroslag ingot. It can be seen that the present invention enables the size reduction of the nitride-based inclusions.

Table 4: Chemical Composition and Inclusion Test Results

Claims (4)

1. A method for refining nitride inclusions in nickel-based wrought superalloy is characterized in that the chemical composition range of the method comprises the nickel-based wrought superalloy in the Standard of GB/T14992-2005 superalloy and intermetallic compound superalloy class and trade mark and other non-Standard trade marks of nickel-based wrought superalloy; the specific process steps are as follows:

(1) surface pretreatment of raw materials: performing surface pretreatment on metal raw materials of blocky pure nickel, pure chromium, pure cobalt, pure tungsten, pure molybdenum, pure niobium, pure aluminum, pure titanium and pure iron; pretreating in a 5vol.% hydrochloric acid aqueous solution to remove surface oxides, wherein the pretreatment time is 20-30 min; then placing the mixture in absolute ethyl alcohol for ultrasonic treatment, wherein the treatment time is 10-20 min; the purity of each raw material is more than 99.9%;

(2) vacuum induction melting: weighing various metal raw materials and other non-metal raw materials in the step (1) in proportion, and carrying out vacuum melting; after being completely melted, the mixture is poured into a steel mould to obtain a high-temperature alloy electrode;

(3) vacuum electroslag remelting: taking the electrode obtained in the step (2) as a consumable electrode, and using CaF with the mass ratio of 0.9: 1-1.1: 1₂With TiO₂Preparing an arc striking agent; slag materials are pre-melted and then are laid at the bottom of the crystallizer; the weight of each slag charge is 3-5 wt.% of the weight of the electrode; vacuumizing to 0.01-100 Pa, and then filling high-purity argon to 0.01-0.06 MPa; slagging and arcing; the arc striking current is 800-1500A, the normal smelting current is 2000-3000A, and the voltage is 35-45V;

the slag charge proportion in the step (3) is 10-30 wt.% CaO and 10-30 wt.% Al₂O₃0.01 to 0.5wt.% MgO, the balance CaF₂(ii) a Proportioning and uniformly mixing slag system raw materials, and then melting at 1300-1700 ℃ for 10-30 min to ensure the uniformity and clarification of liquid slag; pouring into a metal mold for cooling; mechanically crushing and screening to obtain the granularity of 1-15 mm; baking at 600-800 deg.C for at least 8h before use.

2. The method for refining the nitride inclusions in the nickel-base wrought superalloy according to claim 1, wherein the vacuum induction melting step in the step (2) comprises: firstly, putting Ni, Cr, Co, W and Mo metal blocks with low affinity with O, N into a crucible for vacuum induction melting, wherein the crucible is made of alumina; vacuum-pumping to 5 × 10^-1Pa~5×10^-3Pa, smelting; c is added after the melt is melted down, and refining is carried out for 15-30 min; adding strong nitride and oxide to form elements Nb, Ti and Al, and heating until the added materials are completely melted; filling argon to 0.01-0.06 MPa, adding easily burnt and volatile trace elements B and Zr, and stirring simultaneously until the mixture is completely dissolvedAnd pouring the alloy liquid into a steel die after the alloy liquid is completely melted again.

3. The method for refining nitride inclusions in ni-based wrought superalloy according to claim 2, wherein the crucible in step (2) has an MgO content of less than 0.0010 wt.%.

4. The method of refining nitride inclusions in Ni-based wrought superalloy according to claim 1, wherein the Ni-based wrought superalloy is produced with nitride inclusions having a maximum size of 6 μm and an average size of less than 3.3 μm.

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